1. Field of the Invention
The present invention relates to rotary shaft seals which prevent lubricants associated with shaft bearings from leaking externally of the bearing housing or bearing support as well as for preventing foreign particles in the environment from working themselves through the seal into the lubricant. In particular, the present invention is directed to labyrinth and other dynamic type rotary shaft seals designed for such purposes.
2. Description of Related Art
Typical labyrinth type rotary shaft seals are shown in Rockwood, et al. U.S. Pat. Nos. 4,572,517; and 4,022,479, 4,114,902, 4,175,752, 4,304,409, 4,706,968, and 4,466,620, all to Orlowski. In such typical labyrinth type seals, internal labyrinth type grooves are provided in a metal seal ring which is fixed to a bearing housing. These grooves are specifically contoured to create an hydraulic dam effect that acts to remove lubricants moving axially along the shaft and pass them back into the bearing housing. Additionally, such labyrinth type seals are provided with sealing rings for preventing material from moving internally into the housing. However, a problem associated with this type of conventional seal is that there is no complete seal between the internal and external sides of the seal so that some material is permitted to move through the seal into the bearing housing. Furthermore, since the sealing ring wears due to the rotation of the shaft relative to the sealing ring, eventually a state is reached where sufficient foreign particles have entered into the housing which leads to damage of the shaft bearings. Furthermore, labyrinth type seal designs are ineffective when shaft conditions exist such as misalignment (a condition where the center line of the shaft is displaced perpendicularly with respect to the center line of the bore of the bearing seal) and runout of the shaft (a condition where a radial rotational eccentricity exists due to bearing wear, shaft bending or warping, etc.).
As an alternative to the labyrinth groove type seal, rotary shaft seals are known which utilize a seal member that is disposed within a seal housing and which has one or more flange-like lips biased into engagement with a wall of the seal housing. However, since the sealing member is fixed onto the periphery of the rotating shaft so as to rotate with it, high frictional forces are created at the interface between the free end of the flange-like lip and the nonrotating wall of the housing against which it is biased. Examples of such shaft seals can be found in Otto U.S. Pat. No. 3,368,819; Romero U.S. Pat. No. 4,428,586; Johnston U.S. Pat. No. 4,462,600; Toyoda, et al. U.S. Pat. No. 4,465,285; Wehrfritz, et al. U.S. Pat. No. 4,565,378; and Symons, et al. U.S. Pat. No. 4,572,516. With such seals, even if centrifugal forces are utilized to vary the contact force of the flange-like lip against the housing so as to reduce the contact force with increasing shaft speed (see, for example, the above-indicated Toyoda, et al. and Symons, et al. patents), ultimately sufficient wear occurs as to defeat the effectiveness of the seal to such an extent as to require replacement thereof. On the other hand, while it has been proposed to have a flange-like seal lip serve as a contact seal only when the shaft is stationary or rotating slowly, the lip being lifted from the housing wall against which it engages upon a predetermined increase in the rate of shaft rotation (see the above-mentioned Wehrfritz, et al. patent), such a seal has required the use of a compressed gas to lift the flange-like lip and prevent the ingress of foreign matter at higher speed conditions. Such a seal also requires a labyrinth arrangement to prevent the ingress of compressed gas into the bearing and the egress of lubricant from the bearing, at such increased shaft rotation speeds, creating a costly and complicated sealing arrangement.
Thus, there is still a need for a bearing seal for rotary shafts which can be simply and economically constructed, yet will effectively eliminate both the movement of bearing lubricant from the seal housing and the movement of foreign particles into the bearings and lubricant from outside of the housing, and have a long wear life.